After all that had not gone the way Lee had wanted in the Maryland campaign in September 1862, why did Lee not return south across the Potomac, but face the AoP under McClellan at Sharpsburg? Many things about that campaign didn't go as planned: having to fight/seige at Harper's Ferry rather than take it easily, the fact that western Marylanders were lukewarm at best with their support, the Special Order 191 mishap. Why didn't Lee cut his losses and head back south, especially since, if McClellan hadn't dithered, he could have trounced Lee at Antietam?

Harpers Ferry was defended by anything from 10,000 to 14,000 troops (depending on which account you read)led by an inept Colonel, Dixon S Miles, who failed to set adequate defences, but would Lee have known that and really expect to take the place easily? He sent Jackson who himself had commanded there at the beginning of the war and knew the ground but a stronger Union command could have put up a much stiffer resistance.
Did Lee know that a copy of Special Order 191 was in Union hands?
Having fought McClennan on the Peninsular I think one thing that Lee did know was that he would be up against some good fighting men in the AotP but they would be led by a dithering commander.

He didn't know he'd be unable to generate support in western Maryland until he passed through the area.

It's also my understanding that he wasn't aware of the Lost Orders incident until he read about it several months hence in a Yankee newspaper.

And Jackson's capture of Harpers Ferry was hardly a hindrance at all. Harpers Ferry is pretty undefendable, commanded as it is by Bolivar, Loudon and Maryland Heights. It's just not a good place to be since it limits movement of the defender. As one Yankee wrote, Harpers Ferry 'is no more defensible than a well bottom.' The surrender of Dixon Miles' men was the largest capitulation of U.S. troops to that time until the fall of Corregidor in WWII.

The one thing that Lee knew was that he was going against McClellan, and that would probably be enough.

Somewhere (wish I could remember where) I read that Lee was surprised that "dithering" McClellan was able to reorganize and meet him at Antietam in days rather than weeks, as his past experience with McClellan made him think.

I'm thinking, too, that maybe Lee, being Lee, just wanted to fight rather than heading back. He had it in his head to, so he was going to.

Pvt. C., glad to see you made it back from YOUR venture into Northern territory in one piece!

This isn't really adding to the conversation, but kind of seconding what Pam said. I think that Lee was a stubborn, confident man. When he made up his mind and was ready to fight, that is what he was going to do.

All good stuff! Although I think Lee had been alerted to some surprisingly rapid movements (maybe not the Lost Orders, but certainly unexpectedly rapid movements) so he sent off to concentrate on the hills north and east of Sharpsburg.

But I think most are in agreement that Lee wasn't going to march that far to just turn tail and re-cross the Potomac. It would have been the prudent thing to do, but how would that look in terms of public morale? In terms of his and McClellan's soldiers' morale? His soldiers would have been chagrined at losing without a fight. McClellan's soldiers would have broken the losing streak they'd developed over the year.

Political considerations alone were enough to demand a test of strength. Then, there is that his personal pride prohibited retreat.

i believe lee stay and fought along the antietam because macclellan suddenly started acting like a combat leader {the lost order]lee had to retreat from his gains and he might just not wanted to be bested by mac-risking his small force with his back to the potomac was a big gamble but mac didnt dissapoint-if they hadnt had fought units piecemeal and the 5th corps go in-lee very well might have destroyed his army i wonder if he fights there against grant?

I think Ole hit the nail on the head. The Antietam Campaign was as much about political gain as it was about tactical gain. From that stand point it was a bust almost as soon as it began. Marylanders didn't welcome Confederate liberation, the AOP was manuvering agressively, and Bragg's simultanious invasion of Kentucky was not going well either. The ANV had to fight to salvage somthing from a disapointing campaign and maintain its momentum. Cheers!

you need to look at the reasoning for the Invasion of Maryland. First The Confederate Government was looking for European Reconition had Lee or Bragg won a Major Battle North of the Potomac or North of the Tennessee State Line Jeff Davis hoped that France and England would officially reconize them as a legitimate country much like the Battle of Saratoga had done in 1778. Second was that Western Maryland Supported the Confederacy the intentions were to see if it was possible to sustain a major army in the Area long enough to cut Supply line to and from Washington and the Midwest. Third is the Larger Stragety which Includes Bragg's invasion of Kentucky, Sterling Price and Earl Van Dorn at Corinth, and Lee's Invasion of Maryland the hope was that Maryland and Kentucky would secceed from the Union. Maryland is where Washington is and had the state secceeded around the Nations Capital it would have been horrible for the Lincoln Administration and possibly force the Governers of Pennsylvania, Ohio, Indiana, Illinoise, and New York to beg for peace (these states provided the Army with most of its troops.)